Most of the energy consumed in large buildings is due to air conditioning. In commercial and industrial buildings this can be as high as 40-60% of the total energy consumption.

Most large air conditioning systems use chillers to cool water to a fixed temperature. The water flows through pipes and coils and with air blowing across the coils, cools the air in a room. The room thermostat stops cooling by stopping the flow of air or cold water through the cool water coils. Irrespective of the indoor room temperatures, the chiller is left running, keeping the water at the same cooled temperature and resulting in wasted energy.